The objective of this study was to evaluate thecryopreservation of in vitro mature or immature oocytes by conventionalmethod. The experiment was conducted using oocytes of cows' ovaries from slaughterhouse,distributed into six treatments: unfrozen oocytes with the cumulus oophoruscells (T1) and naked (T2) which were submitted to theprocess of MIV, FIV and CIV; immature oocytes, with the cumulus oophoruscells (T3) and naked (T4), which were submitted to thecryopreservation, unfrozen and the MIV, FIV and CIV; oocytes with the cumulusoophorus cells (T5) and naked (T6), which were submittedto in vitro maturation, cryopreservation, and FIV and CIV. The oocyteswere frozen by the conventional methods, dehydrated by the immersion in threesolutions with 0.6; 1.2 and 1.8 mol L-1 of Ethylene Glycol (EG) during5 minutes each phase. The thawing phase was done by the immersion in water-bathat 30 ºC during 20 seconds, and so, the oocytes were re-hydrated in three phases(0.9 mol L-1 EG + 0.3 mol L-1 of sacarose; 0.3 L-1of sacarose without EG and sacarose) for six minutes each one. The mainly ultrastructuralchanges in cryopreserved matured oocytes were prematurely released of corticalgranules. However, the frozen immature and mature oocytes showed vacuolizationand disappearance of cristae mitochondrial. The frozen immature oocytes showedthe maturation rate of 82.5, 75.4, 9.2 and 5.8% for T1, T2,T3 and T4, respectively. The fecundation rate were 56.2,0.0, 38.7, 8.6, 63.6 and 16.7% and from the cleavage were 36.3, 7.9, 0.4, 0.0,0.0 and 0.0% for T1, T2, T3, T4,T5 and T6, respectively. Morula and blastocyst were observedonly for unfrozen and naked oocytes (T1) (34.5%). These results showedthat the frozen protocols affect the viability of the oocytes.
